The subject invention relates to a method for producing a porous titanium material article. Porous means a porosity between 10 and 90 vol. %.
Such an article can comprise both a 3-dimensional and a 2-dimensional article. As example for a 2-dimensional product a support for a photocatalyst is given or a product in which a large surface area is required. Other non exhaustive examples are electrodes, capacitors, fuel cells, electrolysers, structural parts and the like.
Processing massive titanium is generally known in the art and no difficulties are encountered presently.
This is different for producing porous titanium. It is possible to obtain porous titanium which has however a very limited strength. In the above applications high porosity, high surface area; corrosion resistance and weight are of importance as well as good mechanical properties.
In the prior art porous titanium has been produced by sintering titanium metal powder. At elevated sintering temperature the titanium powder is very sensitive to a clean atmosphere during processing. It has been found that titanium powder is very aggressive at elevated temperature resulting in a surface layer for example a titanium oxide or titanium carbide layer. As soon as such a layer or an other layer is formed sintering is hampered because adhesion of adhesive powder particles is impaired.
To solve this problem it is proposed in the prior art to add hydrogen gas during sintering. In this way a reducing atmosphere can be obtained. However it has been found that even if hydrogen is added as a gas still sintering of powder particles is far from optimum resulting in poor mechanical properties of the final porous product.
U.S. Pat. No. 4,206,516 discloses a method for providing a porous surface layer on a cast titanium substrate. To that end a slurry of pure titanium hydride is provided on the substrate. By thermal decomposition titanium hydride particles convert in titanium metal. The slurry is provided by spraying. Because pure titanium hydride particles are used, quite some shrinkage is to be expected after sintering.
U.S. Pat. No. 2,254,549 discloses a composition comprising 60–90% of a base metal not being titanium, a low melting temperature binder, which can comprise copper and titanium and metal hydride. The binder will be present in the final product.
U.S. Pat. No. 3,855,638 discloses a surgical prosthetic device whereon a solid metallic material substrate a porous coating is adhered. The coating is realized starting from an aqueous slurry which is dried and sintered in a hydrogen atmosphere.
U.S. Pat. No. 3,855,638 discloses a surgical prostetic device whereon a solid metallic material substrate a porous coating is adhered. The coating is realised starting from an aqueous slurry which is dried and sintered in a hydrogen atmosphere.
U.S. Pat. No. 3,950,166 discloses the use of either titanium or titanium hydride and no mixtures thereof. The abstract of the Japanese patent specification 2000-017301 discloses a sintered compact which is not porous because of a higher than 95% sintered density. A high percentage (35–95 wt %) titanium hydride powder is added to titanium powder.
U.S. Pat. No. 5,863,398 discloses a method for realising an object by sputtering.
The subject invention aims to provide an improved method for producing a titanium material article having increased mechanical properties.